Criminals and terrorists frequently conceal security threats, such as weapons, explosives, contraband, illicit drugs, under their clothing and in body cavities, when entering security-controlled areas. These security threats must be detected on persons entering such high security areas as prisons, airports, government buildings, nuclear power plants, military bases, and the like. However, searching individuals by hand is time consuming, often ineffective, and objectionable to both the person being screened and the security officer performing the screening.